- Provide status information about the cluster and allow you to use the ndb_mgm for various maintenance tasks like taking a hot backup
- Own the cluster config file (therefore it must be running to start a node)
- Arbitration in case of a potential split-brain
So while the management node can be down, it is nice to have a redundant one for failover. This is very easy to do:
- Add 2 [NDB_MGMD] sections to config.ini:
#Id is required when defining multiple mgmt nodes
- Change the ndb-connectstring to include both IPs of the management nodes:
- Make sure the config.ini is on both management nodes and that the files are identical. Start both ndb_mgmd nodes.
That's it! The management nodes will act in an active-passive way and failover as necessary. Make sure you do not run any management node on the same physical host as a data node - it will cause a cluster shutdown if they fail simultaneously.